Assays are important for diagnosis because they can indicate bacterial infections, viral infections, poisoning, overdose, and so forth. Most assays have to be done in a laboratory and cannot be done in the home, where patients can benefit from the convenience and the privacy. To be effective in Third World countries where medical doctors and laboratories are scarce, the assays need to be done anywhere and anytime. Similarly, in times of disaster or in a war zone, the same mobile requirements must be met.
The reason that most assays cannot be mobile is that stationary machines perform the analysis. These machines can be cabinet size down to bench top size. They are expensive and need AC wall power. The technology in the machines (e.g., flow cytometry, polymerase chain reaction, immunoassays, etc.) is poorly suited to be converted into a mobile implementation.
In recent years, mobile assays have been developed to detect influenza and Human Immunodeficiency Virus (HIV). These tests are qualitative and cannot provide a quantitative measurement of the entity in question. For example, the therapy for a human with HIV is based upon its concentration.